Body weight gain induced by atypical antipsychotics: an extension of the monozygotic twin and sib pair study.

BACKGROUND AND OBJECTIVE: In our original study based on five monozygotic twin pairs and seven same-sex sib pairs, we previously showed that genetic factors contribute to body weight gain induced by the atypical antipsychotic clozapine. We aim to study this further by including patients treated with the atypical antipsychotics olanzapine or risperidone as well as opposite-sex sib pairs. METHODS: Twin and sib pairs were identified by a telephone screening. Measured data on weight and other clinical variables were obtained cross-sectionally and retrospectively from medical records. In seven monozygotic twin pairs and 12 sib pairs (total number of patients treated: n = 38, mean age 29.5 +/- 9.5, range 13.7-54.3 years), the similarity in BMI (kg/m(2)) change under these atypical antipsychotics (atypical Delta BMI) and upon additional inclusion of BMI change under prior antipsychotic medication (total Delta BMI) was explored. RESULTS: For total Delta BMI we found greater similarity in antipsychotic-induced BMI change in MZ twin pairs than in sib pairs (intrapair difference) with a heritability of h(2) = 0.6, but not for atypical Delta BMI, possibly because of a genetically influenced weight plateau achieved under antipsychotic medication. CONCLUSION: The results of the present and our previous report suggest a contribution of genetic factors in antipsychotic-induced weight gain of 60-80%.